Combine the white wine vinegar, white wine and shallots in a
small saucepan over medium heat. Simmer until the liquid is reduced
to about 2 tablespoons. Strain out shallot and discard, return
liquid to the pan.
Stir the wasabi and soy sauce into the reduction in the pan.
Over low heat, gradually whisk in butter one cube at a time
allowing the mixture to emulsify. Be careful not to let the mixture
boil. When all of the butter has been incorporated, stir in
cilantro, and remove from heat. Pour into a small bowl, and set
aside.
Heat a large skillet over medium-high heat. Brush tuna
steaks with olive oil, and season with salt and pepper. Place
in the hot skillet, and sear for 3 to 5 minutes on each side. Be
careful not to overcook, this fish should be served still a little
pink in the center. Serve with sauce.
